Hitherto, a so-called coated type magnetic recording medium has been widely used. The coated type medium has been prepared by dispersing a magnetic powder of oxides such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, F.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, Bertholide compounds of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, Co-doped Bertholide compounds or CrO.sub.2, or a ferromagnetic alloy powder mainly composed of Fe, Ni or Co in an organic binder such as copolymer of vinyl chloride and vinyl acetate, a copolymer of styrene and butadiene, an epoxy resin or a polyurethane resin to obtain a coating solution, coating the resulting magnetic coating composition on a non-magnetic support and drying to form a magnetic film.
Recently, with the increase in the amount of information to be recorded, practical use of a magnetic recording medium which is suitable for high density recording has been greatly desired. Attention has been drawn to a so-called thin film type magnetic recording medium which is prepared by forming a ferromagnetic thin metal film on the above described support in accordance with methods such as a vacuum deposition method, a sputtering method, an ion plating method or a metal plating method without using the above described binders. Further various attempts have been made through extensive research and development to put the products into practical use.
However, a ferromagnetic thin metal film tends to corrode easily. This is a serious problem which affects reliability as a medium, and the means to solve the problem has not yet been found.